In feed processing production, the process is usually divided into raw material receiving and cleaning crushing, batching, mixing, pelletizing, finished product packaging and other sections. Among them, batching and mixing are two independent sections, requiring separate batching scale and mixer. The process is complex, equipment investment, occupies a large space. Foreign companies have a number of batching, mixing two types of equipment combined into one, which can give full play to the efficiency of the equipment, reduce costs. China's research in this area is basically in the development stage, the main existence of dosage and mixing cycle is long, low dosage precision, high residue in the body. To address this situation, our institute in the national "Ninth Five-Year" science and technology research project "feed processing new key equipment development" completed the development of rapid weighing mixer.

In the selection of the mixing body using a single-axis pulp leaf mixer, which has a biaxial mixer mixing time is short, high mixing uniformity, but the price is cheaper than the biaxial mixer, covers an area of small, easy to arrange the process. As the system adopts high-speed feeding device, frequency control, air volume automatic correction and other control technologies, improve the dosing accuracy and speed. The level of domestic leading.

1 Fast weighing mixer system introduction

The system consists of single-axis paddle mixer, high-speed feeding mechanism, weighing module, dosage weighing instrument and corresponding control software.

1.1 Main technical performance indicators

Dosing mixing cycle ≤ 5min dosing accuracy of 0.2% (F.S); mixing uniformity (CV) <5%; mixing time ≤ 2min; dosage of not less than 14 types.

2 mixer structure form

Single-axis paddle mixer is a new type of mixing equipment, which has strong adaptability to materials, short mixing time and high mixing uniformity. The novel and reliable discharge gate structure ensures that the mixer is fast and efficient, and it is cheaper than the double-axis mixer.

2.1 Test conditions Test material: corn flour

Material moisture: 15.2%

Powder particle size: crushed sieve aperture in 2.5mm

3 high-speed feeding device and control

For fast weighing mixer, its main feature is high-speed feeding, through high-speed feeding to shorten the dosing time to improve the hourly output. For the dosage accuracy, with the increase of dosage speed, the dosage accuracy will decrease. And dosing accuracy is the key to determine product quality. So the speed and accuracy is a pair of contradictory body, how to make the two combined into the best state, change the contradiction into a unity, this is the key technology. The design scheme is as follows.

3.1 Adopt single and double winch feeding

For the large proportion of materials (such as corn, bran, etc.) fast feeding with a double-girder feeding at the same time, slow feeding with a single-girder feeding, so that the large proportion of materials feeding (batching) time is shortened by half.

3.2 Adopt frequency conversion control technology

The working frequency of the motor is between 50~60Hz for fast feeding, and between 5~10Hz for slow feeding. The application of this technology ensures the high speed feeding while taking into account that the batching accuracy is not affected.

3.3 Adopting air volume automatic correction technology

For the addition of various small ratio materials, due to the addition of components in the addition of the mixer can not be subtracted, so it is necessary to use advance control to stop feeding in a timely manner for feeding control, that is, weighing control instrumentation to automatically detect the feeding mechanism to stop feeding the amount of air as the next control of the advance, to avoid adding the amount of excess, in order to improve the accuracy of the control.

3.4 Special design of the feeding winch new design of the feeding winch so that the material can be more uniformly discharged at the exit to improve the accuracy of the dosage.

4 feeding system

Mixer in the running time within the material is constantly tumbling, because the material fluctuations caused by the vibration will be transmitted to the weighing module, so that the weight displayed on the weighing instrument to produce a jump in weight (even if there is no material in the mixer). The larger the jump value, the worse the dosage accuracy. So the weight of the mixture is inevitable. Therefore, in addition to the equipment design and installation to take the necessary measures, in the feeding system software, hardware must also take special solutions. Through repeated experiments to study the mixer no load, full load point and load the weight of each weighing point jump range, to find out which with regularity of the mathematical model, and accordingly the software and hardware weight stability filtering processing.

4.1 Instrument software and hardware processing

The instrument hardware adopts active filter processing, and the software adopts multiple balancing to find intermediate value operation, rolling digital filtering technology, and the filtering constant can be set.

4.2 Design of weighing instrument

The design and development of weighing instrument integrates the application of microcontroller, microelectronics technology, high-resolution fast analog-to-digital conversion (ADC) and many other technologies. For the serious industrial site of multiple types of electromagnetic interference and other conditions, the instrument uses a variety of hardware and software anti-disturbance technology. In addition to the use of conventional hardware isolation transformers, passive filters, active low-pass filters, weighing small signal shielding and grounding technology, but also on the analog input/output and switching volume using a primary or secondary photoelectric isolation and other anti-interference measures. A variety of digital filtering algorithms and rolling digital filtering algorithm technology are adopted in software to make the weighing display value more accurate and stable, which ensures that the system can run stably and safely for a long time.

4.3 Selection of weighing accuracy and drift of accuracy

In order to make the weighing accuracy and precision drift of the weighing display and control instrument reach or exceed the national standard, the analog circuit of the instrument selects precision resistors with ultra-low temperature drift, high-precision amplifiers and ADC devices, and the coupling weighing module adopts the advanced six-wire system technology, differential balancing input and software zero position auto-tracking technology, so as to make the weighing accuracy of the instrument stable for a long period of time, and reach the national measurement technology standard. 4.4 System software

The system software includes functions of data acquisition, data processing, data control, fuzzy control, alarm monitoring and communication.

4.4.1 Data acquisition and processing program

The data acquisition program is to collect the sensor data through the weighing instrument, and then get the corresponding frequency value through the V/F converter. The frequency value is proportional to the displayed weight value, and the scale factor is determined through a large number of tests and then through statistical data processing. In order to ensure the accuracy of the sampling data and improve the control precision, the collected data first need to be filtered by the software to filter out the transient interference, and then through the nonlinear correction to get the correct data.

4.4.2 Control program

The control program adopts closed-loop control, which decides to adjust the feeding mechanism according to the comparison between the sampling value and the set control parameters. Due to the inertia of the feeding mechanism, pure closed-loop control cannot accurately control the feeding time and the response speed cannot keep up with it, thus resulting in overshooting phenomenon. For this reason, the new software adopts the control method of fuzzy control theory, and the program firstly tracks the weight change, predicts the trend of the weight change, and generates the advance control amount to exclude the influence caused by inertia. However, this amount of advance is an uncertain amount. After a large number of experimental tests, a -set of fuzzy control process is obtained. According to the predicted amount, the fuzzy control method suitable for the current state is automatically selected. With this method to control the feeding mechanism, and then with the inverter control, so that the feeding mechanism is no longer like the previous only constant speed operation, but analog continuous control, thus solving the problem of difficult to control the amount of feed to ensure that the system control accuracy, to achieve the final design requirements.

5 Conclusion

After the application of fast weighing mixer system, the dynamic dosing accuracy is improved from 0.3% (F.S) to 0.2% (F.S). The mixer has high mixing uniformity and low material residue during production, which improves product quality and increases product competitiveness. In addition, the system saves space height of about 3m compared with the previous similar equipment, the infrastructure cost of plant construction can be reduced accordingly, and the process design is more flexible. Due to the simplicity of the equipment, production costs and equipment maintenance costs also fell to improve the economic efficiency of enterprises. In addition, the system does not have the previous scale body, thus avoiding the scale body to open the door to spray material affecting the environment and improve the labor environment. The results are not only used in the feed industry, but also can be widely used in other industries such as powder making.